Buying in bulk - things you replace often!

Hi, I am looking after the servicing of about 5 bikes for other people and was wondering if anyone could point me in the right direction for bulk buying for cable inners and outers, tubes etc...etc...the stuff you replace often.

I found a site in the states where you can buy 10 inner gear cables and 20 metres of outers, but they wanted $47 for postage and the purchase was only $51.

Cheers

Andrew